The present invention relates generally to the field of semiconductor devices and, more particularly, to techniques for determining characteristics of semi-insulating gallium arsenide for use as substrate material in the manufacture of integrated circuits.
As is well known, semi-insulating gallium arsenide (GaAs) is used as a substrate material for GaAs integrated circuits. Nominally undoped, semi-insulating, liquid encapsulated Czochralski (LEC) grown GaAs contains deep donor defects compensated by shallow acceptor impurities which are primarily carbon ions. The impurities affect the performance and characteristics of electronic devices and integrated circuits fabricated on such substrates of GaAs. Specifically, the pinch-off voltage of ion-implanted n-channel field-effect transistors fabricated on semi-insulating GaAs substrates has been correlated with substrate acceptor impurities. The current method of assessing acceptor impurity concentrations is to measure the carbon concentration by using secondary ion mass spectroscopy (SIMs) analysis. This method is time consuming, requires expensive equipment and does not measure all the acceptors which may be present.